How do bones heal / repair themselves?

Answer 1

When a bone breaks, a blood clot forms and bone demolition cells near the site of the break immediately begin clearing away the rubble. Meanwhile, the bone creates a sort of patch called a bone callus to replace the blood clot and hold the broken bone together. At the same time, bone construction cells near the break start to produce new bone material to repair the damage. Depending on the bone and the severity of the fracture, after several weeks its hardworking cells can repair a broken bone as good as new.

Answer 2

I'll send you the site this came from. It's very interesting the phases the bone goes through in the healing process.


Bone healing
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X-ray of a bone fracture in the process of healing.Bone healing or fracture healing is a proliferative physiological process, in which the body facilitates repair of Bone fractures.

Contents [hide]
1 Physiology and process of healing
1.1 Phases of fracture healing
1.1.1 Reactive Phase
1.1.2 Reparative Phase
1.1.3 Remodeling Phase
2 Other forms and complications
2.1 Inadequate bone healing
3 Medical Treatments
3.1 Osseointegration
4 References
5 Notes
6 External links



[edit] Physiology and process of healing
In the process of fracture healing, several phases of recovery facilitate the proliferation and protection of the areas surrounding fractures and dislocations. The length of the process is relevant to the extent of the injury, and usual margins of two to three weeks are given for the reparation of the majority of upper bodily fractures; anywhere above four weeks given for lower bodily injury.

The process of the entire regeneration of the bone can depend upon the angle of dislocation or fracture, and dislocated bones are generally pushed back into place via relocation with or without anaesthetic. While the bone formation usually spans the entire duration of the healing process, in some instances, bone marrow within the fracture having healed two or fewer weeks before the final remodeling phase.

While immobilization and surgery may facilitate healing, a fracture ultimately heals through physiological processes. The healing process is mainly determined by the periosteum (the connective tissue membrane covering the bone). The periosteum is the primary source of precursor cells which develop into chondroblasts and osteoblasts that are essential to the healing of bone. The bone marrow (when present), endosteum, small blood vessels, and fibroblasts are secondary sources.


[edit] Phases of fracture healing
There are three phases of fracture healing which are separated into 5 total phases;

Reactive Phase

Fracture and inflammatory phase
Granulation tissue formation
Reparative Phase

Callus formation
Lamellar bone deposition
Remodeling Phase

Remodeling to original bone contour

[edit] Reactive Phase
After fracture, the first change seen by light and electron microscopy is the presence of blood cells within the tissues which are adjacent to the injury site. Soon after fracture, the blood vessels constrict, stopping any further bleeding.[1] Within a few hours after fracture, the extravascular blood cells, known as a "hematoma", form a blood clot. All of the cells within the blood clot degenerate and die.[2] Some of the cells outside of the blood clot, but adjacent to the injury site, also degenerate and die.[3] Within this same area, the fibroblasts survive and replicate. They form a loose aggregate of cells, interspersed with small blood vessels, known as granulation tissue.[4]


[edit] Reparative Phase
Days after fracture, the cells of the periosteum replicate and transform. The periosteal cells proximal to the fracture gap develop into chondroblasts and form hyaline cartilage. The periosteal cells distal to the fracture gap develop into osteoblasts and form woven bone. The fibroblasts within the granulation tissue also develop into chondroblasts and form hyaline cartilage.[5] These two new tissues grow in size until they unite with their counterparts from other pieces of the fracture. This process forms the fracture callus.[6] Eventually, the fracture gap is bridged by the hyaline cartilage and woven bone, restoring some of its original strength.

The next phase is the replacement of the hyaline cartilage and woven bone with "lamellar bone". The replacement process is known as "endochondral ossification" with respect to the hyaline cartilage and "bony substitution" with respect to the woven bone. Substitution of the woven bone with lamellar bone precedes the substitution of the hyaline cartilage with lamellar bone. The lamellar bone begins forming soon after the collagen matrix of either tissue becomes mineralized. At this point, "vascular channels" with many accompanying osteoblasts penetrate the mineralized matrix. The osteoblasts form new lamellar bone upon the recently exposed surface of the mineralized matrix. This new lamellar bone is in the form of "trabecular bone".[7][8][9] Eventually, all of the woven bone and cartilage of the original fracture callus is replaced by trabeclular bone, restoring much, if not all, of the bone's original strength.


[edit] Remodeling Phase
The remodeling process substitutes the trabecular bone with "compact bone". The trabecular bone is first resorbed by osteoclasts, creating a shallow resorption pit known as a "Howship's lacuna". Then osteoblasts deposit compact bone within the resorption pit. Eventually, the fracture callus is remodelled into a new shape which closely duplicates the bone's original shape and strength.[10]


[edit] Other forms and complications

[edit] Inadequate bone healing
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Inadequate bone healing may predispose to further fractures at the same site, as well pseudarthrosis, undesired mobility in what appears to have become a new joint.

Many factors may contribute to lack of bone healing, including smoking (nicotine is known toxin for bones)[1]


[edit] Medical Treatments
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Many treatments may be employed to stimulate bone healing. A few treatments include: - Bone morphogenetic proteins (BMP) are used to stimulate formation of new bone growth in areas such as with a spinal fusion. - Sex - During sexual intercourse and/or stimulation of the genitalia small amounts of BMP are released into the blood stream. - Electrical stimulation - either external or internal - may be used to stimulate bone growth and healing after a spinal fusion - Surgery to immobolize the bone may be used in certain instances to help a fracture heal. For example, with a spinal fracture, vertebroplasty or kyphoplasty may be used to immobolize a vertebra and create a better healing environment.


[edit] Osseointegration
Osseointegration is the pattern of growth exhibited by bone tissue during assimilation of surgically-implanted devices, prostheses or bone grafts to be used as either replacement parts (e.g., hip) or as anchors (e.g., endosseous dental implants).


[edit] References
Brighton, Carl T. and Robert M. Hunt (1986), "Histochemical localization of calcium in the fracture callus with potassium pyroantimonate: possible role of chondrocyte mitochondrial calcium in callus calcification", Journal of Bone and Joint Surgery, 68-A (5): 703-715
Brighton, Carl T. and Robert M. Hunt (1991), "Early histologic and ultrastructural changes in medullary fracture callus", Journal of Bone and Joint Surgery, 73-A (6): 832-847
Brighton, Carl T. and Robert M. Hunt (1997), "Early histologic and ultrastructural changes in microvessels of periosteal callus", Journal of Orthopaedic Trauma, 11 (4): 244-253
Ham, Arthur W. and William R. Harris (1972), "Repair and transplantation of bone", The biochemistry and physiology of bone, New York: Academic Press, p. 337-399

[edit] Notes
^ Brighton and Hunt (1997), p. 248: The extravascular blood cells are identified as erythrocytes, platelets and neutrophils.
^ Brighton and Hunt (1991), p. 837: The cells within the clot are identified.
^ Brighton and Hunt (1997)
^ Ham
^ Brighton and Hunt (1997), p. 248: Two light micrographs showing the cells of the woven bone and hyaline cartilage.
^ Brighton and Hunt (1986), p. 704: Two light micrographs of a typical fracture callus: one showing the tissues and the other showing the cells.
^ Brighton and Hunt (1986)
^ Brighton and Hunt (1997)
^ Ham
^ Ham

I hope this helped you.